Open Graph URL that isn't absolute

<meta property="og:image" content="/images/cover.jpg"> looks correct from inside the site: the path resolves, the file exists, and the page renders. But Open Graph values aren’t read by a browser on your page. They’re read by a scraper that fetched your HTML to build a link preview somewhere else, and to that scraper /images/cover.jpg doesn’t point anywhere.

Why avoid

The protocol defines these values as absolute URLs. The Open Graph protocol’s type table says a URL is “All valid URLs that utilize the http:// or https:// protocols”. Its machine-readable schema gives the type as “a string of Unicode characters forming a valid URL having the http or https scheme”, and assigns it to og:url, og:image, og:video and og:audio. A path like /cover.jpg, a bare cover.jpg, or a scheme-less //cdn.example.com/cover.jpg is not a value of that type.

og:url is the object’s identity, not just a link. Open Graph defines it as “the canonical URL of your object that will be used as its permanent ID in the graph”, and Facebook’s webmaster guide calls it “the canonical URL for your page”. A relative ID means nothing outside the document it was written in, so shares of the same page stop being recognised as one object.

A consumer that follows the protocol has nothing to resolve a relative value against, so it treats it as invalid or absent. The share card appears without its image or video, or with one the scraper guessed. It fails silently: the page looks fine in every browser, and the broken card only shows up when someone shares the link. How each platform handles an invalid value isn’t documented. A site that ships relative values is relying on leniency nobody promised. Facebook’s Sharing Debugger shows “which meta tags the crawler scrapes as well as any errors or warnings” for a given URL.

Use instead

<meta property="og:url" content="https://example.com/posts/my-post">
<meta property="og:image" content="https://example.com/images/cover.jpg">

Build them from the site’s origin when the page is rendered. In JavaScript, use new URL(path, "https://example.com").

Detectability

Fully detectable. The selector picks out the four URL-typed base properties whose content doesn’t already begin with http:// or https://. The logic then trims surrounding whitespace and reports any value that still doesn’t. A missing content is reported too. Structured variants such as og:image:secure_url share the type but aren’t covered, and neither is the common name="og:image" mistake.

There is no autofix: making a value absolute needs the site’s origin, which the markup doesn’t carry.

Resources

• The Open Graph protocol — Types — URL: “All valid URLs that utilize the http:// or https:// protocols”; og:url as the object’s permanent ID.
• Open Graph schema — ogp.me.ttl — ogc:url, “a valid URL having the http or https scheme”, as the range of og:url, og:image, og:video and og:audio.
• Meta for Developers — A Guide to Sharing for Webmasters — og:url is the page’s canonical URL; the Sharing Debugger shows what the crawler scrapes and its errors.